1. Field of the Invention
The present invention relates to an air bag ignition control apparatus for an automotive vehicle and the control method therefor, and more specifically to an air bag ignition control system and the method of discriminating slight collision from serious collision or vice versa by use of a single shock sensor.
2. Description of the Prior Art
The air bag expansion apparatus is used to protect a vehicle driver from shock generated when the vehicle collides against an object. In more detail, at vehicle collision, shock is detected by plural shock sensors and a valve of a high pressure gas vessel is opened by gunpowder usually to supply high pressure gas into the folded air bag for air bag expansion. That is, the air bag apparatus is usually composed of an air bag, a gas generator, a gas ignitor, shock sensors, etc.
To facilitate understanding of the present invention, collision mode will be first explained. In general, vehicle collision can be classified into either a slight collision or a serious (pole) collision. The slight collision is a collision mode in which an air bag is not required to be expanded as when a vehicle travelling at a relatively low speed collides head-on against a wall, for instance. In this slight collision mode, strong members provided within an engine room will not be deformed to absorb a shock, and therefore a shock applied to a bumper is transmitted to a vehicle room without time delay, with a result that deceleration sensors arranged within a vehicle room output detection signals, respectively each of whose detection signal levels increases uniformly in waveform shape. On the other hand, the serious (pole) collision is a collision mode in which an air bag is required to be expanded as when a vehicle collides against a pole-like obstruction, for instance. In this serious collision mode, the strong members provided within the engine room are first deformed to absorb shock and thereafter a secondary shock due to engine movement is applied to the vehicle room. In this mode, therefore, a shock applied to the bumper is transmitted to the vehicle room without time delay and thereafter another shock is applied to the vehicle room; with a result that deceleration sensors arranged within the vehicle room output detection signals, respectively each of whose detection signal levels increases uniformly in waveform shape for a while after collision but increases sharply after a predetermined time has elapsed. However, under some conditions there exists a problem in that the waveform of the sensor output signal at the serious collision is similar to that at the slight collision within a predetermined time after collision, as when the vehicle collides obliquely against a wall.
To overcome the above-mentioned problem in the prior-art air bag ignition control apparatus as disclosed in Japanese Published Unexamined (Kokai) Patent Appli. No. 55-19627 or Japanese Published Unexamined (Kokai) Utility Model Appli. No. 55-47602, a plurality of deceleration sensors connected in parallel to each other are arranged at the bumper and within the vehicle room, separately, so that an ignition signal can be outputted to expand the air bag whenever any one of the deceleration sensors detects a deceleration rate beyond a predetermined value.
In the above-mentioned prior-art air bag ignition control apparatus, however, since a plurality of deceleration sensors are required, there exists another problem in that the parts and the assembly cost are both relatively high.